1. Field of the Invention
The present invention relates to a control device of a multi-cylinder 4-cycle charge (homogeneous charge or stratified charge) compression ignition-type internal combustion engine that performs charge compression ignition combustion in which air-fuel mixture formed in a combustion chamber is compressed and is ignited by itself.
2. Description of the Related Art
It is considered that, to reduce an amount of NOx generated by combustion in an internal combustion engine, self ignition combustion that air-fuel mixture is ignited by itself by compressing the air-fuel mixture of an extremely lean air-fuel ratio formed in a combustion chamber and is combusted in extremely short time is useful. In a homogeneous charge compression ignition-type internal combustion engine that performs the self ignition combustion, knocking is hardly caused even if air-fuel mixture is highly compressed, compared with air-fuel mixture in an internal combustion engine using spark ignition. Therefore, reduction of fuel consumption is also expected by combusting the highly compressed air-fuel mixture.
To combust air-fuel mixture by self ignition, it is necessary to increase the temperature of the air-fuel mixture. In prior arts, therefore, air-fuel mixture used for combustion is formed by mixing high-temperature combustion gas with air and fuel. The amount of combustion gas required for igniting the air-fuel mixture by itself generally increases as the amount of air required increases according to a driving state.
Japanese Patent Application Laid-Open (kokai) No. 1999-132066 (claim 1, FIGS. 1 to 4) discloses an engine that simultaneously takes air and combustion gas to utilize combustion gas for forming air-fuel mixture. In this disclosed art, when two intake valves are opened and air is taken into a combustion chamber, one of two exhaust valves is opened. Hereby, combustion gas remaining in an exhaust path is taken into the combustion chamber together with the air. In the engine, however, as the air and the combustion gas are simultaneously taken into the combustion chamber, the combustion gas taken into the combustion chamber interferes with the air taken in. Therefore, for example, when a large amount of air is preferentially obtained due to a large load of the internal combustion engine, the amount of combustion gas becomes insufficient compared with a desired amount. As a result, self ignition combustion may become unstable. Further, since the engine takes combustion gas remaining in the exhaust path into the combustion chamber by the decrease of pressure (cylinder pressure) in the combustion chamber by the increase of the volume of the combustion chamber in an intake stroke, a large amount of combustion gas cannot be taken.
As described above, in the prior art, the amount of air and combustion gas which can be taken into the combustion chamber is limited. Therefore, it is difficult to realize stable combustion by self ignition in a wide operating range.